Technical Field
The present disclosure relates to the field of water purification and specifically to an organic-templated-boehmite-nanoarchitecture (OTBN) used for water purification.
Technical Background
Availability of clean drinking water is a major health concern across the world, especially in the developing and under-developed countries. Amongst the major contaminants which contaminate water, the major ones include biological (e.g. bacteria and virus), inorganic (e.g. fluoride, arsenic, iron) and organic (e.g. pesticides, volatile organics) species. Various governmental initiatives across the world continue to support the projects to ensure availability of clean drinking water to the people of respective countries. However, it continues to be a major problem because technological costs, in many cases, continue to stay above affordable limit which eventually affects the poor as they are unable to afford clean drinking water.
The fact that poor continues to suffer due to un-availability of clean drinking water is common across various statistics collected by various sources. It is therefore important to make a technological intervention to improve the affordability of available state-of-the-art technologies. This can go a long way in improving the health of people globally.
Aluminum-based compositions have been exhaustively studied for the removal of inorganic anions, such as fluorides and arsenates from drinking water. Use of aluminum-based compositions is more pertinent for fluoride adsorption from water due to its relatively higher fluoride adsorption capacity vis-à-vis other adsorbents. Moreover, aluminum-based compositions do not require any additional pre/post-filtration. Various improvements in the capacity of aluminum-based compositions have been proposed till date. Practically, all aluminum-based compositions in the field use require frequent regeneration, largely to reduce the cost of water purification. However, traditionally followed practice of regeneration, i.e., alkali treatment followed by acidification, leads to secondary contamination of water sources caused due to high fluoride concentration in the sludge, leaching of aluminum in water and high dissolved salt content of the sludge. Prior art related to fluoride removal using aluminum-based compositions and associated challenges are covered in detail in our previous Indian patent application 1529/CHE/2010, entire contents of which are herein incorporated by reference.
The Indian patent application 1529/CHE/2010 describes a method to produce aluminum oxyhydroxide-chitosan composite at room temperature. There are a number of advantages in the adsorbent composition, including green chemistry based preparation at room temperature, binder free granulation, ease of filter-ability/wash-ability and an easy-to-adapt method for preparation of mixed metal hydroxides/oxides.
It was reported that an adsorbent dose of 500 mg/L is sufficient to remove fluoride concentration below 0.5 ppm, when input fluoride is varied from 1-10 mg/L. The aluminum oxyhydroxide-chitosan composite exhibits a fluoride adsorption capacity of over 53 mg/g at an initial fluoride concentration of 10 mg/L in deionized water. Owing to the presence of competing anions in ground water, the fluoride adsorption capacity of the composition diminishes and an adsorbent dose of 1.5 g/L is required to remove fluoride concentration below 0.5 ppm, when input fluoride concentration in ground water is varied from 1-10 mg/L. Cost of the material is approximately Indian Rupees 350 per kg. This translates to a material cost of Indian Rupees 5 per 10 L (assuming a household requires 10 L of fluoride free drinking water per day).
Further, the following prior art documents have attempted to develop various fluoride removal techniques using aluminum and/or chitosan based compositions:    1. Miretzky P., Cirelli A. F., Fluoride removal from water by chitosan derivatives and composites: A review, Journal of Fluorine Chemistry 132 (2011) 231-240;    2. Jagtap S., Yenkie M. K., Das S., Rayalu S., Synthesis and characterization of lanthanum impregnated chitosan flakes for fluoride removal in water, Desalination 273 (2011) 267-275;    3. Fluoride removal from water by adsorption—A review, Bhatnagar A., Kumar E., Mika Sillanpää M., Chemical Engineering Journal, 171 (2011) 811-840; and    4. Liu R., Gong W., Lan H., Gao Y., Liu H., Qu J., Defluoridation by freshly prepared aluminum hydroxides, 175 (2011) 144-149.
While the prior art methods and compositions are effective in fluoride removal from water to a large extent, there exists a scope for improvement. For example, even the reduced cost of the adsorbent composition is still too high for some of the Indian households. Mainly, it is expected that the water purification composition satisfies the following conditions:
Firstly, the adsorbent composition should be implementable at the household level, i.e., it should exhibit high adsorption kinetics and low empty bed contact time. Secondly, the adsorbent composition should require no regeneration, and thus should not generate any secondary contamination. Thirdly, the adsorbent composition should be easy-to-use and maintain, i.e., it should not require any pre/post-filtration. Fourthly, the adsorbent dose should be able to reduce any input concentration that is below 10 ppm to below 1 ppm, as per the Indian National Sanitation Foundation norm for water to be used for fluoride removal. Finally and most importantly, the cost of water purification should not exceed Indian Rupees 3 per 10 L of purified water (Le., the composition should be affordable) and the quantity of adsorbent should not exceed 2-3 g per 10 L of purified water.
In light of the foregoing discussion, there exists a need to address the aforementioned problems and other shortcomings associated with the prior art methods and compositions. These needs and other needs are satisfied by the water purification composition of the present disclosure. Considering the widespread contamination of fluoride across the globe, the water purification composition of the present invention will have a major positive effect on the health of the society as it can be used to provide point-of-use water filters.